Technical Abstract:
Rhizoctonia crown and root rot (RCRR), caused by Rhizoctonia solani AG 2-2, is a common root disease on sugar beet that reduces yield and sucrose during the growing season and causes further losses by increasing respiration and reducing sucrose content during storage. The industry needs to identify the respiration and sucrose concentration changes associated with different levels of severity of RCRR to minimize sucrose losses during storage and also determine when fields should be abandoned. In 2010 and 2011 roots in five RCRR categories (0-1, 2, 3, 4, and 5 =healthy to a few non-active lesions, <5, 6-25, 26-50, 51-75 % root rotted, respectively) were collected from plots inoculated with R. solani. Roots were washed, placed in perforated plastic bags, stored at 4.4 °C and 90-95% R.H, and measured for respiration rate 30, 60, and 90 days after harvest (DAH) and sucrose concentration 30 and 90 DAH. At 30 DAH, respiration rates were 3.5, 3.4, 3.7, 4.4 and 6.3 and 3.5, 3.7, 3.7, 4.3 and 7.1 mg kg-1 hour-1 in 2010 and 2011, respectively, for RCRR ratings of 0-1, 2, 3, 4 and 5, respectively. At 30 DAH, extractable sucrose concentrations were 307, 304, 296, 276 and 240 and 310, 293, 296, 265 and 214 lb ton-1 in 2010 and 2011, respectively, for RCRR ratings of 0-1, 2, 3, 4 and 5, respectively. Overall, impact of RCRR during storage was minimal at disease ratings of 0-3, but increased at higher disease ratings.